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Need a crash course on gas engines

R/C Submarine modelers

Postby ThierryC » Fri Feb 20, 2004 11:38 pm

Hi all

I am not familliar at all with gas engines, however for my next project I want to include one possibly 2 of these in my sub. I would need someone to teach all the basic about them, how small can they be ? rpm ? prices ? gear boxes like a car ? etc.....

Thanks, I can be contacted by email or MSN.
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Postby Carcharadon » Sat Feb 21, 2004 1:48 pm

Thierry, let me see if I understand this correctly. Your model submarine is going to have a gas engine coupled to a former motor now electric generator which in turn will charge the batteries maintaining full charge without overcharging and the batteries in turn powering the electric motor (s) to run the sub. If this is the plan or close to it I think it is one heck of an experiment. I guess a voltage regulator could take care of the overcharging problem. In the case where the batteries are fully charged the voltage regulator would simply keep the generator from producing excess power until needed. So this seems reasonable. Keeping the gas engine running would require a compressed source of air and a small gas regulator. Also, like the simple governor on a lawnmower the gas engine would be set to run at say a middle throttle and the governor would adjust for loading from the generator and adjust throttle to the engine as needed. The exhaust gas could be simply dumped from the sub or possibly used to power a turbine to turn the prop or even another generator! Starting the gas engine could be done I suppose with either a pull cord or electric start. I'm thinking small 2cycle (lawn edger). Also a large model sub. All this seems possible in theory but as a practical matter very complex. Very interesting though, good luck.
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Postby ThierryC » Sat Feb 21, 2004 2:37 pm

Hi there
I plan on having one gaz engine running both propellers when the boat is surfaced, and at the same time turn a generator. When I dive, the gas engine would shut off, and the sub would switch to a pair of electric engines. If possible, (depending on the size of the gas engine) I would use a gas engine for each driveshaft.
Or if this is too complex, I would basically have the same setup than a real type XXI: The prop shafts are always powered by 2 electric engines. When on the surface, or snorkeling, a gas engine would turn a generator, charging the gel-cel.
I know the running time gained from that will probably be minimal, but I enjoy the challenge of building a system like that that would work.
:D
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Postby Captain Nemo12 » Sat Feb 21, 2004 2:55 pm

I always knew that someone would experiment with a system like that, I don't know how you would do this but making the gas engine recharge the batteries once on the surface is pretty similar to a u-boat's diesel engine system, maybe you use a snorkel? :p
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Postby Carcharadon » Sat Feb 21, 2004 3:47 pm

Thierry, that sounds pretty good, by just running the gas on the surface you eliminate the compressed air problem and regulator problem. I think possibly with one gear reduction from the gas motor you could power the two shafts. But then the electric motor would have to turn the gas engine (this would be a big waste of power) unless you could decouple the gas engine somehow. It seems like for this concept to work most of your effort would be in obtaining or building the gear reduction/transmission. As a starter I would just go with the generator on the surface and electric motors. Sounds like a fun project.
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Postby ThierryC » Sat Feb 21, 2004 4:42 pm

When running at periscope depth I will just use a snorkel, when fully surfaced, I will use the regular air intakes on the sides of the tower.
For the connection between the electric engines and the gas engines I am thinking of using an electro-magnetic brake, but I don't know one would be powerfull enough.
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Postby ThierryC » Sat Feb 21, 2004 5:13 pm

So, who could tell me about gas engines ?
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Postby Carcharadon » Sat Feb 21, 2004 5:17 pm

The clutch in your ac compressor in your car is such a device, it works well. That’s the concept I’d try. But making one? Some of these magnetic type couplers never actually touch. In a chemistry lab they use a plastic coated bar magnet to stir things up, some water pumps in aquariums function on the same principal. When the gas engine is running it would have more than enough power to generate a sufficient field between two plates without ever touching, then when switched to battery power current to the magnet coupler off or diminished so that – gas engine disconnected. In theory sounds good. Even if plates seperated by only .001" at least no moving parts.
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Postby Dolphin » Sat Feb 21, 2004 5:49 pm

Thierry,

Contact Skip Asay.

Steve
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Postby Novagator » Sat Feb 21, 2004 6:15 pm

the gas engines for airplanes and gas car require an electric starter that is a good size, you will need to fashion and electic starter to crank the engine, you might be better off with a scale v8 motor that works with an electric starter on it.

I can't see how an engine from an airplane model would work.

What about a turbine? :D
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Postby Novagator » Sat Feb 21, 2004 6:22 pm

Here are some working gas V8s that can be started electrically, but they $5,000 each for a 1/4 scale.

http://www.conleyprecision.com/prod01.htm

If you plan on using one like this

Image

You can use an onboard starter

Image
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXCGR0&P=0

I didn't know they made such an animal.
:p
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Postby ThierryC » Sat Feb 21, 2004 8:29 pm

For that price I might aswell get a Chevy 350 engine :-)
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Postby Novagator » Sat Feb 21, 2004 9:25 pm

ThierryC wrote:For that price I might aswell get a Chevy 350 engine :-)

it would be cheaper.
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Postby Atomic Subs » Sun Feb 22, 2004 1:15 am

Thierry,

I didn't see if this was mentioned but, your going to need to
find a way to seal your main air induction and exhaust for diving, maybe large solenoids that won't choke down your air intake and exhaust. Remember, you'll need lots of air and the last thing you want is to suck in water on the compression stroke when you stop the gas motor!

I've seen this happen on $25,000.00 marine diesels and it's
not a pretty site... makes grown men cry!

Lyle
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Postby KOEZE » Sun Feb 22, 2004 10:03 am

Hi Thierry,

I'd say the optio with the engine and generator always connected with a boat driven by electric motors is the best option. Most realitic too. For the gas engine you could use one like this.Image It features an electic starter. To stop the it you could cut the air (you need to do so in order to keep it from flooding) or put a disc brake between the gas engine and the generator. A bicycle brake could do miracles too.

There is also the possibility to use a model car clutch which uses cetrifugal force to connect the crankshaft with a drive shaft.
Image

Keep us posted.

EJK
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you get older because you stop playing.
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